Bimetal blade



April 5 G. s. FARISON 2,707,216

BIMETAL BLADE Filed Jan. 21, 1953 2 6162222 Sig/Q2 155;???

W ag/ United States Patent BIMETAL BLADE Glenn Shuler Farison, Logansport, Ind., assignor t0 Essex Wire Corporation, Logansport, Ind., a corporation of Michigan Application January 21, 1953, Serial No. 332,263

7 Claims. (Cl. 200138) My present invention relates to thermo-responsive actuators and more specifically to a new and improved bi: metal blade for an automatic reset, snap action type of actuator.

The bimetal blade of my present invention finds particular utility in circuit breakers wherein snap action of a thermo responsive switch element having a characteristic automatic reset feature is desirable. Briefly the blade of my present invention embodies certain improved features and details of construction resulting in means for main taining contact pressure between a stationary and a movable contact until the build up of reversal forces, caused by thermo response of the material of the actuating blade, results in snap action of the blade to open circuit through the contacts. One of the outstanding features of the blade of my invention resides in the arrangement of certain portions thereof whereby thermo response of the bimetal thereof to ambient temperature causes a cantilever spring action of the blade to take place which serves to increase contact pressure between a circuit contact carried by the blade and a stationary contact mounted adjacent the blade. This initial cantilever reaction of the blade followed by thermal reaction thereof to snap the blade to an open position is brought about by the arrangement of the blade elements in a manner whereby certain portions thereof are heated at a greater rate than the remainder thereof. The initial cantilever reaction of the blade is also designed to continue for a suilicient period until reversal of forces occurs in the blade to cause a snap reversal of its normal curvature. This snap action is then utilized to effect opening between the stationary contact terminal and the movable contact carried by the blade. Further, as is normal in most bimetal actuators of this class, when the thermal forces causing the reversal of the blade are dissipated the formation stresses in the bimetallic structure thereof cause a reestablishment of its normal and original rigid state. This return of the blade automatically upon dissipation of the thermal forces is utilized to effect closure between the stationary terminal contact and the contact carried by the blade. The outstanding advantage of the blade of my instant invention resides in its ability to maintain sustained positive contact pressure between the contact carried by the blade and its stationary terminal contact until the point of actual thermally induced reversal of the blades curvature takes place. This feature does much to eliminate blade flutter and thereby assures a clean make and break type of circuit interrupter.

The main object of my present invention is to provide a new and improved bimetal actuator especially adapted for thermal responsive control devices in which means is embodied for assuring positive contact pressure up to the instant of thermal reversal of the blades curvature.

Another object of my invention is to provide a bimetal blade having improved features of construction and operation whereby blade flutter and intermittent contact of circuit contacts associated therewith is substantially eliminated.

Still another object of my present invention is to provide a new and improved bimetal blade for use in thermal control devices having particular features of construction whereby initial reaction of the bimetal blade to ambient temperature causes an actual increase in contact pressure between a circuit contact carried by the blade and a stationary contact.

A still further object of my invention is to provide a new, improved and simply constructed bimetal blade for thermal responsive actuators having improved operating characteristics.

The above and further objects and features of my present invention will be recognized by one familiar with the art and will be more fully understood and appreciated from the following detailed description and specification thereof in conjunction with the accompanying drawings.

In the drawings:

Figure l is an exploded perspective of the blade of my present invention associated with a schematically represented mounting base of a switch assembly;

Figure 2 is an enlarged side elevational view of the assembly illustrated in Figure 1 showing the blade of my instant invention in closed contact relation with a terminal contact of the switch assembly of Figure 1;

Figure 3 is an enlarged side elevational view, similar to Figure 2 showing the blade of my instant invention in its open circuit condition wherein the contact carried by the blade is spaced or separated from the stationary contact of the switch mounting base.

Figure 4 is an enlarged plan view of the blade of my present invention;

Figure 5 is an enlarged cross sectional view taken substantially along a longitudinal center-line 5-5 of Figure 4 showing the features of formation utilized in my present bimetal blade;

Figure 6 is an end elevational view looking at the right hand end of the blade as seen in Figure 4 and showing the structural features of that end of the blade; and

Figure 7 is an end elevational view, similar to Figure 6, looking at the left hand end of the blade as viewed in Figure 4.

Turning now to the features of my instant invention, and particularly the perspective showing thereof in Figure 1, it will be recognized that a bimetal blade 10 therein is provided for mounting to an insulated switch base 11 having a mounting post 12 and a contact terminal 13. The blade 10 carries with it an electrical contact button 14 for cooperation with a second stationary contact 15 carried by the terminal contact post 13.

As will be recognized from Figures 4 through 7 in particular, blade 10 is substantially rectangular in plan and is provided with an outer portion and an inner portion 21. Outer portion 2il is distorted angularly substantially along its center line as exemplified by line 5-5 of Figure 4 and particularly illustrated in Figure 7 of the drawings. This angular distortion of the outer portion of the blade serves to control the length of time required to reset the blade after thermal forces reversing its curvature have been dissipated. The movable contact 14 is carried adjacent the free end of the outer portion 20 by rigidly attaching the same to the blade. Of course, it will be understood that the material of the blade is bimetal or that is, composed of two thin layers of metal having unlike thermal expansive characteristics fused in a manner whereby each of the layers imparts its individual thermal reaction to the entire blade. Normally one of the layers of such a bimetal material is composed of a substance having a substantially greater coefiicient of thermal expansion than the other layer. In the particular form of blade herein illustrated, the high expansive side of the blade is disposed preferably downward, or that is, on the side on which contact 14 is carried.

Snap action in the bimetal blade 10 is accomplished by dlstorting the same about its outer perimeter through suitable forming and drawing of the metal so that the blade cups or dishes upwardly at the inner portion 21 which in effect causes the outer portion to bound the inner portion with a substantially rigid nature. It will be seen that the blades inner portion 21 is so constructed as to have a freely movable leg member 22 connected at one end to a raised cup portion 23.

Therefore, the free leg 22 of the inner portion of the blade comprises a bimetal cantilever disposed within or bounded by a rigid, distorted bimetal outer portion 20 which carries an electrical contact, as contact 14 illustrated. Leg 22, as is best seen in Figures 1 and 4, extends outwardly toward the center of the blade from the raised cup portion 23 thereof and is bounded by a free opening 24 extending around its periphery. A mounting hole 25 is also provided adjacent the outer end of leg 22 for securing the blade to the top of mounting post 12 of the base member 11. In attaching the leg 22 to the mounting post 12, the vertical distance between the top of the mounting post 12 and the top of the contact terminal 15 is such that in the normal closed position of the blade initial spring loaded contact pressure is established between contacts 14 and 15 when leg 22 is rigidly attached to the top of the mounting post 12 by means of a drive screw or bolt 26. In actual practice leg 22 is slightly flexed in securing the blade to the mounting base and since the leg is relatively flexible in comparison with the rigid outer portion 20, contact pressure is created between contacts 14 and 15. In effect, leg portion 22 constitutes a flat leaf spring and carries consequently a flat spring rate which allows wide variation in contact tolerances without detrimental changes in contact pressures between contacts 14 and 15. This feature is most desirable for easy calibration in production.

The angular distortion of the outer portion 20 of the blade along line 5, as best illustrated in Figures 5 and 7, is maintained and held rigid by extruding the inner portion 21 of the blade upwardly along inclined separated skirt portions 27, 27 to form cup 23 and by turning a lip 28 downwardly at the rearward end of the blade as best seen in Figures 5 and 6. The lip 28 functions to strengthen the back end of the blade against flexing action which occurs by thermal response of the bimetal blade and therefore such maintains consistent rigidity in the blade. Calibration of the blade is closely controlled by regulating the distortion of the outer portion 20 of the blade and especially in drawing two arm sections 30 and 31 simultaneously while performing the described extruding and drawing operations necessary to produce the upwardly raised skirt portions 27, 27 and the inner portion 21 of the blade.

It will further be recognized that the formation of the blade, having the features described hereabove, may be performed in a single fabricating operation while the calibration is performed in a subsequent operation by drawing the two arm sections 30 and 31 toward one another during the extruding and drawing operations.

As will be appreciated from Figure 1 of the drawings, both the mounting post 12 and the contact terminal 13 receive current carrying conductors 34 and 35, respectively. Attachment of the inner portion 21 of the blade and particularly the free end of leg portion 22 thereof to the mounting post 12 is accomplished in a manner, as described above, whereby spring bias is placed on the flexible leg portion 22 to impose initial contact pressure between contacts 14 and 15. Further it will be understood that the circuit controlled by the bimetal actuator of my invention passes through the inner portion 21 of the blade along the outer portion 20 thereof and through the contacts 14 and 15. Since the current carrying inner portion 21 of the blade has much less area than the combined current carrying sectional areas formed by arms 30 and 31 and the outer portion 20 of the blade, the same has consequently greater resistance to current flow which results in more rapid heating of the leg portion 22. As a result the bimetal leg, which has its high expanding side downwardly or next to the support mounting post 12, will assume a curvature dependent on the degree of heat generated in this section during current flow which results in turning moments on a platform of the blades cup portion 23. Such turning moments or couples tend to lower contact 14 carried at the outer or free end of outer portion 20 of the blade thereby increasing contact pressure between contacts 14 and 15. When the current load carried in the blade exceeds the value determined at the blade rating, the rigid section, or that is, the substantially rigid outer portion 20 of the blade will collapse and snap through an unstable pressure point to assume a rigid state of opposite curvature that is reversed from its Figure 2 position, substantially as illustrated in Figure 3 of the drawings. Subsequent cooling of the blade will reestablish normal formation tensions in the blade which will return the outer portion thereof to its original rigid state, as illustrated in Figure 2, bringing contacts 14 and into circuit closing relation. As stated heretofore the length of time required for the blade to reset is controlled by the angular formation of the blade substantially along the length of longitudinal line 55 of Figure 4.

Thus it will be understood and appreciated that I have provided a new and improved device of a snap action automatic reset type employing a bimetal blade designed for use particularly in thermal responsive circuit breakers and like devices and having means embodied therein which provide constant contact pressure between a stationary and a movable contact until the build up of thermal forces results in the snap action reversal of the blades curvature. The many advantages and features of a blade of this character will be readily understood and appreciated by those familiar with the art and as a result suggested changes, alterations and substitutions of equivalents will readily come to mind. Consequently, I do not wish to be limited to the specific form of my invention herein illustrated and described except as may appear in the following appended claims.

I claim:

1. In a thermally responsive circuit protective device, a bimetal actuating blade comprising, an outer blade portion distorted angularly a calibrated amount along its longitudinal center line to form two lengthwise extending planar arm sections, a lip portion turned downwardly at one end of said outer portion for rigidifying adjacent end areas of said blade and fixing the calibrated angularity between said arm sections, the other end of said outer portion being freely flexible in the presence of thermal stresses, a contact carried by said outer portion at its said other end, an inner portion for said blade formed within the boundaries of said outer portion and including, a raised inverted cup portion rigidifying adjacent areas of said outer portion and formed integrally with said lip portion and arm sections, and a cantilever leg member forming a part of said inner portion, said leg member extending in cantilever fashion from the top wall of said cup portion substantially along the longitudinal center line of said blade in overhanging relation with said arm sections, said leg being freely disassociated from said arm sections and outer portion and characteristically flexible as a leaf spring, said leg having means for attaching said blade to a support at a point located within the boundaries of said outer portion and substantially centrally of said blade, the relative areas and flexing characteristics of said leg and outer portion being such that thermal stresses imposed on said blade cause an initial flexing of said leg to move said contact and other end of said arm sections in one direction followed by a snap action of said outer portion to move said contact in an opposite direction.

2. A bimetal actuator for use in thermal responsive circuit protective devices and the like, comprising, a

bimetal blade having a substantially rigid outer portion formed with calibrated transverse curvature, a raised cup portion formed along the longitudinal center line of said outer portion and disposed adjacent one end of said blade, a planar leg portion extending from the bottom wall of said cup portion and disposed within the peripheral confines of said outer portion, said leg portion being substantially flexible with a flat spring rate and having a free extension movable independently of said outer portion and said cup portion, and a downwardly turned lip portion formed transversely of said blade and at said one end thereof for rigidly relating said cup portion and said outer portion and maintaining the calibrated curvature of said outer portion.

3. A bimetal blade for use in thermal responsive circuit protective devices and the like, comprising, an outer portion having planar longitudinal arm sections intersecting angularly substantially along the longitudinal center line of said blade, a rigid cup portion formed adjacent one end of said blade, a thermal responsive cantilever leg portion extending from and to one side of the bottom wall of said cup portion and within the peripheral confines of said outer portion, said leg portion carrying means for the cantilever mounting of said blade to a rigid support and being independently movable of said outer portion in response to current flow in said blade, a lip portion formed along one end of said blade adjacent said cup portion and rigidly interjoining said arm sections thereof and said cup portion for the purpose of maintaining the calibrated angular intersecting relation of said arm sections, and a circuit contact carried by the end of said blade which lies opposite said cup portion for movement with said outer portion in response to thermal reaction thereof.

4. A thermal responsive actuator of the class described, comprising, a unitary bimetal blade member having a pair of integral arm sections defining planes intersecting substantially along the longitudinal center line of said blade, a circuit contact member carried by said arm sections, adjacent one end thereof, a raised rigid cup portion formed at the opposite end of said arm sections, a ip portion related transversely of said arm sections at one side of said cup portion and arranged to maintain the intersecting angularity of said arm sections, and a flexible planar leg portion extending from the bottom wall of said cup portion, said leg portion extending partially along the line of intersection of said arm sections, but separated from the latter and forming a cantilever spring means for mounting said blade to a support.

5. A thermal responsive actuator of the class described, comprising, a bimetal blade having intersecting planar arm sections freely movable at one end in response to thermal influence, a contact member carried at said freely movable end of said arm sections, a raised cup portion formed at the other end of said arm sections, a lip portion formed transversely of said cup portion and arm sections and arranged to maintain the intersecting angularity of said arm sections, and a cantilever leg portion projecting integrally from the bottom wall of said cup portion toward said contact member, said leg portion being separated from said arm sections, thereby movable independently thereof, and having means adjacent its one end for attaching said blade to a rigid support whereby said blade is suspended in cantilever fashion and attached to said support at a point intermediate its ends so that thermal response of the said bimetal leg portion and said arm sections, respectively, causes opposite directional movements of said contact member relative to said support.

6. A thermally responsive circuit protective device of the class described, comprising, a support member, a stationary contact carried by said support member, a bimetal blade mounted in cantilever fashion on said support and overhanging said contact member thereon, a second contact member carried by said blade for engaging said stationary contact, said blade comprising a substantially rigid outer portion having two longitudinally extending and integrally related planar arm sections intersectingly arranged at calibrated angularity, a lip portion turned downwardly at one end of said blade for rigidly interconnecting said arm sections and maintaining their calibrated angularity of intersection, and an inner portio formed within the peripheral confines of said arm sections and comprising a rigid cup having a planar leg element extending from the bottom wall thereof, said leg element being disposed intermediate the ends of said blade, movable independently of said blades outcr portion and comprising a cantilever leaf spring having means adjacent its one end for connecting said blade to said support member.

7. The thermal responsive circuit protective device as set forth in claim 6 wherein the area of said leg portion is substantially less than the area of said outer portion whereby thermal activity of said blade in response to the flow of electrical energy therethrough results in initial reaction of said leg portion causing movement of the free end of said blade in one direction followed by thermal reaction of said outer portion resulting in a snap action movement of said free end in an opposite direction.

References Cited in the file of this patent UNITED STATES PATENTS 2,266,537 Elmer Dec. 16, 1941 2,340,615 Rath Feb. 1, 1944 2,528,756 Kaser Nov. 7, 1950 

